ECT vs PILOTS

[TearlessTom]

We are planning on taking a trip to the Smokies the 1st week of October.     

Most of our riding will be between 2000 - 5000 feet.

I live at sea level and  my bike runs great. I am hoping to be able to complete an ECT mod and Balance the carbs before I leave. (I don't have a carb tool yet so the balance may be put off until I can lay hands on a working solution.)

I have a slight smell of unburned gas from the exhaust now so she may be a bit rich but not sure. I don't get that from my other bikes but then again they don't have 6 carbs.

???????My question is this???????

At higher elevations should I adjust the ECT to advance the spark or just leave well enough alone?

 It seems that I remember during the 1st oil crisis (very crappy gas) I had to retard my timing on an old 1979 Mercury Capri 2.3 liter to keep the dreaded engine knock out because it was running so lean.

So my thinking is leaving the timing in the stock position would be the best solution. 

Is my thinking correct?

I am hoping my slight richness will even out the elevation's leanness.

Thanks in Advance


Tom

[Mikey]

I could be wrong... but i believe as you go up, your mixture gets richer because the air is thinner.

[TearlessTom]

Your right. The curse of being left handed... everything in the world is backwards.

So, Should I advance the ECT?

[Mikey]

I would think it would be safe. 

[John U.]

That's the reason for installing the potentiometer for the ECT mod.
On the other hand you can always run mid grade or high test in case you have a problem. I don't think elevation has an effect on advance but pulling up steep grades with a load and/or two-up may well cause pre ignition on regular.

[TearlessTom]

That's the reason for installing the potentiometer for the ECT mod.
On the other hand you can always run mid grade or high test in case you have a problem. I don't think elevation has an effect on advance but pulling up steep grades with a load and/or two-up may well cause pre ignition on regular.

That was my concern
Thanks
Tom

[ptgb]

I live at 1000 feet... we went to Inzane this year in Colorado with 4 Valks. We rode up to 12,300 feet at the highest and we were commonly between 7000 and 10,000 feet. Two of the Valks were pulling trailers of 400 lbs or so.

Mine (w/trailer), stock, had no problems whatsoever.

Valk (w/trailer) blew a bit of black smoke under load up near 10,000+ feet but nothing was changed and it was fine.

Valk (w/belly tank = fuel pump), fouled one plug... took it out cleaned it, no further problems.

Valk (stock), no problems.

Also, out west Regular Unleaded was 85 octane instead of 87 like here in Ohio.

I wouldn't fiddle with anything, you won't have a problem at the altitudes you are talking about. Just my .02
  

[TearlessTom]

I agree and am not really expecting any problems.  Just wondering which setup would optimize my performance vs milage. I guess in my old age few things in life make my heart flutter like a properly tuned bike.

Tom

[Ricky-D]

I suggest doing nothing at all. If the bike runs good now, it will run good at any altitude. That is the beauty of the CV carburetors. They adjust to the thinner air by lessening the venturi opening. In other words the slide does not rise up as far in relation to the throttle position. Therefore the mixture stays correct in the thinner air. As to changing the spark timing, I would not alter it at all. I run premium gasoline so there is no worry about ignition knock on my end, and if you expect to hear the knock before doing anything about it, well you're too late. You will not necessarily hear spark knock and damage could already have happened.

***

[TearlessTom]

I suggest doing nothing at all. If the bike runs good now, it will run good at any altitude. That is the beauty of the CV carburetors. They adjust to the thinner air by lessening the venturi opening. In other words the slide does not rise up as far in relation to the throttle position. Therefore the mixture stays correct in the thinner air. As to changing the spark timing, I would not alter it at all. I run premium gasoline so there is no worry about ignition knock on my end, and if you expect to hear the knock before doing anything about it, well you're too late. You will not necessarily hear spark knock and damage could already have happened.

***

Okay Ricky, I understand what you are saying and agree that probable nothing needs to be changed.
 But am a bit confused also. With my admitted limited experience with carbs. I have rebuilt a few and re-jeted a few.

None of the following has to do with the timing advancement, that is a whole different ball of wax.

I understand that the opening is varied by the height, but the height is varied by the vacuum from the engine which increases/decreases with speed/rpm.

The air/fuel mixture is regulated by the amount of taper of the needle. As it is raised with the slide the opening becomes larger and more fuel is allowed to mix with more air keeping the mixture constant.

If we look at Boyles Law: Boyles Law "For a fixed amount of an ideal gas kept at a fixed temperature, P [pressure] and V [volume] are inversely proportional (while one increases, the other decreases)."

In other words the speed of the air entering the combustion chamber is the same but the density or total amount of O2 is different.  In this case less.

The vacuum of the engine is a closed loop type circuit so to speak and the air intake/combustion/exhaust is an open liner circuit.

So my confusion / question for you is how does the closed vacuum circuit of the engine know how dense the air is of the open intake circuit?

I don't think it can. That is the whole reason jet kits are made. We tune the amount of fuel to match the density of the air at different altitudes and circumstances.

[RoadKill]

I would NOT touch anything if it is adjusted for your normal altitude. I am at 1000 ft above see level, runs clean and almost lean.
The poor abused old girl got best fuel economy EVER in the rocky mountains at IZ9... And I even saw some fools  on valks doing burn outs at 14,300 ft on top of Mt Evans. Dang Darkside tires always marking their territory I suppose! LOL   

[Ricky-D]

TT,    I'll try to explain why, the best I can.

At altitude the ambient air pressure is less. (means less air for a given area)
At altitude the amount of oxygen is less as a percentage of the total but the difference is negligible.
I guess you could refer to this as density.

You turn the throttle and the butterfly opens.  The slide moves up because there is a variable between the air pressure inside and outside the carburetor.

The air is less dense at altitude so the difference in variation is less so the slide does not rise the same (height) as if you were at a lower altitude.

The result is less gas and less air to the motor.  The motor feels less powerful. It is!  You need more rpms to develop the same power. Maybe it won't ever get there until you get lower in altitude.

You may feel the throttle is cranked way on, but the slide is doing it's own thing, wholly dependent upon the variable.

So now you can say, there "that makes my case" but there is still more.

At altitude where there is less pressure, there is also an affect to the fuel delivery. Remember there is a pressure variable that affects the reaction of the slide. There is the same for the fuel, for it's the variable that makes the gasoline rise up to the jets and out into the venturi area. So at altitude there is a lessening amount of fuel being delivered to the motor via the jets (needles).

If you compare the effect upon the two, air and gas, there is a greater difference dealing with the air and just a slight difference with the gas but taken together the result is a good running motor at altitude due to the incorporation of the CV carburetor and there is no need to re-jet at any altitude.

***

[John U.]

The Honda service manual calls for a "high altitude pilot screw adjustment of 1/2 turn in"
from the normal setting. This is for continuous operation above 6,500ft.